396 University of California Publications in Geology [Vol. 12 



Comparative Length of Metaconid-Metastylid Column in Pliohippus, 



HiPPARION AND MERYCHPPUS 



Ratio of length of crown Ratio of breadth of crown 



to anteroposterior diameter to anteroposterior diameter 



of metaconid-metastylid of metaconid-metastylid 





pillar 



pillar 



No. 23510, Mi 



.56 mm. 



1.19 mm. 



No. 23510, Mj 



.50 



1.21 



No. 23286, Mi 



.60 



1.12 



H. leptode from Eattlesnake 







no. 544, Pi 



.60 



1.22 



H. moliavense no. 19788, Pj 



.62 



1.23 



H. mohavense, type, no. 21348, 







Pj 



.60 



1.10 



Meryehippus, average. Pi .... 



.36-.47 



.77-.93 



Pliohippus, average, Pi 



.50 



.90 



Remarks. — The type specimen represents a somewhat immature 

 individual, being but slightly worn, and not having come into 

 function. of the referred specimen is slightly heavier than that 

 of the type, is in better condition, and illustrates the characteristic 

 points to better advantage. In this specimen (fig. 130) there is a 

 suggestion of a fold on the anterior border of the hypoconid of P5 

 as seen in a Rattlesnake specimen (Univ. Calif. Coll. Vert. Pal. no. 

 544). The parastylid is moderately well produced. The entoconid is 

 remarkably full and round. The groove of the elongated metaconid- 

 metastylid column is deeper in and much less flat than in M^. 

 These specimens are but very tentatively referred to P. osborni, sub- 

 form A. 



MEDIUM SIZED LOWER TEETH, NEAE ( ?)PLIOHIPPUS EDENSIS, n. p. . 



Material. — A left ramus containing Pj to Pi, no. 23195 (figs. 1326, 140), Univ. 

 Calif, loc. 3269; and associated series representing Pj to Mi, no. 23194 (figs. 133, 

 141c), Univ. Calif, loc. 3267; premolars, nos. 23231 and 23784 (figs. 135a-135b); 

 Pj, nos. 23214 and 23209 (fig. 134o-134b); molars, nos. 23215 (figs. 136a, 141a), 

 23201, 23211 (figs. 136b-136c) ; molars, nos. 23352 (figs. 137a, 141b), 23226, 24283 

 (figs. 137b-137c); M3, nos. 23230, 23287 (figs. 138a-138&); two very worn molars 

 in jaw fragment, no. 23289 (fig. 139). All specimens in Univ. Calif. Coll. 

 Vert. Pal. 



Characters. — The medium sized and generalized Pliohippus form ; 

 exterior faces of protoconid and hypoconid convex; groove between 

 metaeonid and metastylid column shallow and open ; the moderate 

 anteroposterior length of wings of metaconid-metastylid column, which 

 is greater in premolars than in molars. 



